复制代码 代码如下:

<script type="text/javascript">

function Ajax(){

var xhr;

if(window.XMLHttpRequest){

xhr=new XMLHttpRequest();

}else{

try{xhr=new ActiveXObject("MSXML2.XMLHTTP.6.0");}catch(e){}

try{xhr=new ActiveXObject("MSXML2.XMLHTTP");}catch(e){}

}

if(!xhr) return;

this.Xhr=xhr; //用属性存储XMLHttpRequest对象的实例

}

Ajax.prototype.send=function(url,options){

if(!this.Xhr) return;

var xhr=this.Xhr;

var aborted=false;

var _options={ //提供默认值

method:"GET",

timeout:5000,

onerror:function(){},

onsuccess:function(){}

};

for(var o in options){ //覆盖掉原来的默认值

_options[o]=options[o];

}

function checkForTimeout(){ //检查是否超时的情况

if(xhr.readyState!=4){

aborted=true;

xhr.abort(); //取消本次传输

}

}

//在规定的时间内检查readyState属性的值

setTimeout(checkForTimeout,_options.timeout);

function onreadystateCallback(){

if(xhr.readyState==4){

/*

* 注释：状态码在200内表示成功，300内表示重定向，400内是客户端错误，500是服务器端错误

*/

if(!aborted && xhr.status>=200 && xhr.status<300){ //检查aborted属性是否超时

_options.onsuccess(xhr);

}else{

_options.onerror(xhr);

}

}

}

xhr.open(_options.method,url,true);

xhr.onreadystatechange=onreadystateCallback;

xhr.send(null);

}

var ajax=new Ajax();

ajax.send("test.php",{method: GET ,timeout:100,onerror:onerror,onsuccess:onsuccess});

function onerror(xhr){

alert("Timeout");

}

function onsuccess(xhr){

alert(xhr.responseText);

}

</script>